1. Field of the Disclosure
The present disclosure relates generally to apparatus and methods for formation fluid collection and testing.
2. Description of the Related Art
During both drilling of a wellbore and after drilling, fluid (oil, gas and water) from the formation is often extracted to determine the nature of the hydrocarbons in hydrocarbon-bearing formations. Fluid samples are often collected in sample chambers and the collected samples are tested to determine various properties of the extracted formation fluid. To drill a well, drilling fluid is circulated under pressure greater than the pressure of the formation in which the well is drilled. The drilling fluid invades into the formation surrounding the wellbore to varying depths, referred to as the invaded zone, which contaminates the original fluid present in the invaded zone. To collect samples of the original fluid present in the formation, a formation testing tool is conveyed into the wellbore. A pump typically extracts the fluid from the formation via a sealed probe placed against the inside wall of the wellbore. The initially extracted fluid is discarded into the wellbore while testing it for contamination. When the extracted fluid is sufficiently clean, samples are collected in chambers for further analysis. Single and concentric probes have been proposed for extracting formation fluid. In concentric probes, separate pumps are used to extract fluid from the formation via an outer probe and an inner probe. The outer probe extracts the fluid present around the inner probe, which aids in removing the contaminated fluid more efficiently and may prevent fluid from the wellbore to flow into the inner probe. When the contamination level is at an acceptable level, the fluid from the inner probe is pumped into sample chambers, while the fluid from the outer probe is discharged into the wellbore or into a sample chamber for analysis.
Current formation testing systems typically utilize two or more pumps to perform specific functions, such as to extract fluid from the formation. Such systems utilize a single (or common) hydraulic bus or line to supply pressurized fluid to operate hydraulically-operated devices, such as the pumps, flow control valves and other devices. During operation, it is desirable to independently operate some of the devices coupled to the single hydraulic line and/or turn on some, but not all, of the devices. It is also desirable to turn on and turn off such devices when needed to maintain desired pressure in the common hydraulic line to save energy used for pumping the pressurized fluid.
The disclosure herein provides a formation evaluation system that allows independent operation of two or more pumps using a common hydraulic bus.